Gluthatione S-transferase gene family in Citrus sinensis

We report on the characterization of the gluthatione S-transferase (GST) genes in Citrus sinensis L. Osbeck through a systematic EST data-mining. We identified 61 GST transcripts, described the full or the partial length nature of the sequences and defined, for each sequence, the GST class membership exploiting the GST classification schema from Arabidopsis thaliana. In addition, tissue expression profiling (i.e. SemiQ RT-PCR analysis) was undertaken to assess GST expression patterns in various organs/tissues and in two different genotypes: a pigmented (blood) and a non-pigmented (common) sweet orange cultivar. SemiQ RT-PCR assays demonstrated that the most of the C. sinensis GST transcripts, reconstructed via in silico analysis, were active and the transcript abundance of some GST transcripts was 'tissue-affected'. The present study provides basic information and reference data concerning the C. sinensis GST family and will pave the way for elucidating the role of sweet orange GSTs.
Glutathione S-transferases (GSTs; EC 2.5.1.18) are an ancient and ubiquitous gene family encoding ~ 25- to 29-kD proteins that form both homodimers and heterodimers in vivo. Historically, GST enzymes were first discovered in animals in the 1960s for their importance in the metabolism and detoxification of drugs. Their presence in plants was recognized shortly afterwards, in 1970, when a GST activity from maize was shown to be responsible for protecting the crop from injury by the chloro-S-triazine atrazine herbicide. Thereby GSTs were thought as detoxification enzymes, which are liable for the inactivation of toxic chemical compounds by catalysing their conjugation to glutathione (GSH). The result of this process is less toxic and more water-soluble molecules, which are then recognized and transferred across membranes for excretion or sequestration by ATP-dependent membrane pumps. In animals, this mechanism allows their excretion from the body, while in plants, glutathione S-conjugates are sequestered in the vacuole or transferred to the apoplast (storage excretion). GSTs recognize not only reactive electrophilic xenobiotic molecules (i.e. drugs or herbicides) but also compounds which are of endogenous origin. In plants, many secondary metabolites are phytotoxic, even to the cells that produce them, and thereby the targeting to the vacuole is crucial.

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